i had the same or at least a similar problem. Regardless of the master volume output, I always had a kind of background noise on all outputs, i.e. headphones and line outs even if the master volume output was "0". In addition, there was a signal in the high frequency range that was only visible after I played a sound.
i have attached the frequency spectrum of the broken device and a small video that shows what was happening after I had played any sound. But regardless of what the frequency spectrum showed, the background noise could always be heard.
I tried to re-import the firmware, to reset the device and to recalibrate it. unfortunately nothing helped.
Solution: i had to exchange the device. and now everything is fine. no more rushing at all and no strange signals in the frequency spectrum either. now the rev2 sounds perfect and 100% clean.